The prohibition against the use of polychlorinated biphenyls (PCB's) as dielectric fluids, because they constitute an environmental hazard, has resulted in an extensive search for suitable substitutes. A good dielectric fluid should not burn, should be fluid over a wide range of temperatures, should be environmentally acceptable, should be inexpensive, and, or course, should have good electrical insulating characteristics. Fluids which have been used to replace PCB's include silicones, phthalate esters, alkylated aromatics, and hydrocarbons. All of these fluids, and indeed any fluid, is a compromise of desirable and undesirable properties. Fluids which excel in one characteristic may be deficient in another desirable characteristic. Generally, there are minimum standards that a fluid must meet, however, which are set by the industry and/or government, before it will be accepted.